It has previously been suggested to directly mine metal values from sulfide ores. While theoretically the idea is quite feasible from an engineering standpoint, previous attempts to accomplish such electrochemical mining met with limited success. Initially, the reaction would proceed as theorized, but after only a relatively short application of electric current to the ore body, the electrodes would polarize due to the buildup of an insulating shield of sulfur on the surface of the ore. Current efficiencies would rapidly deteriorate and the electrolysis would slow to an unacceptable rate. Continued application of electrical energy would soon result in total polarization of the electrodes and termination of the electrolysis.
Attempts to overcome this problem have been previously made. It has been suggested that the sulfur buildup and consequent polarization could be eliminated by heating the electrolyte solution to a temperature in excess of the melting point of the sulfur, i.e. above 119 degrees centigrade, thereby melting and extracting the sulfur being built up by a Frasch type process, Such a process, of course, has its obvious shortcomings and difficulties. More particularly, the necessity for maintaining high temperatures below the earth's surfaces with the consequent heat loss places a substantial economic burden on the process with only a very limited return. More elaborate heating and sealing means are required, and these present real engineering and economic difficulties. While such difficulties can be overcome, they are only done with substantial increases in cost, the value of which cannot be justified by the relatively limited sulfur values which can thus be recovered. The sulfur thus recovered cannont compete economically with sulfur conventionally mined by the Frasch process.
Various electrolytes have also been suggested for use in previous attempts to directly recover metals from earth deposits by electrolytic processes. It is recognized that as in any electrolytic process, a conductive solution is required. In the electrolysis of sulfide ores, once the electrolysis is initiated with a conductive electrolyte solution, various salt forming ions enter the electrolyte thus changing the electrolyte composition and forming electrolytes of various concentrations of sulfate and metal ions. As such, it was previously suggested to form the initial electrolyte with sulfate salts or any of the various other inexpensive conductive salts including sodium chloride. Such electrolytes, while useful for initiating the electrolysis, failed to insure continuation of the electrolysis and soon resulted in polarization of the electrodes.
It is an object of the present invention to provide a means for the direct mining of sulfide ore deposits from subterranean ore bodies by electrochemical techniques.
It is a further object of the present invention to provide a method which eliminates polarization of electrodes due to sulfur buildup.
It is another object of the present invention to provide an economical method for the recovery of metal values directly from subterranean sulfide deposits at higher current densities, at economically feasible commercial rates and on a long term basis.
Yet another object of the present invention is to provide an electrochemical process for the mining of sulfide ores which eliminates waste disposal problems, surface water pollution, air pollution and other environmental contamination normally associated with the mining of sulfide ores.
Yet a further object of the present invention is to provide a process for the electrochemical mining of metal values which provides flexability in extracting metal values in a variety of alternatives which can be applied to yield metal values directly as metals or as commercially usable metal salts.
These and other objects of the present invention will become readily apparent to those skilled in the art from the description of the invention which follows.